Investigation of Bulk Solid Thermal Properties with Application to an Effective Heat Recovery Mechanism for Lunar Soil

Lunar regolith is characterized by very low mechanical strength and thermal conductivity due to the small inter-particle contact area and the vacuum environment. This poses challenges to future lunar exploration effort involving thermal processing of lunar soil to extract useful resources. The low thermal conductivity leads to low efficiency for heat recovery, and thus bigger equipment size, which is likely one of the limiting factors for manned exploration at larger scale with longer duration. This paper describes an experimental and analytical study of bulk solid thermal conductivity taking into account of the effect of properties of base solid, the filler gas, void fraction, and the vacuum conditions. A semi-empirical model has been developed that can be plugged into a proprietary solid-to-solid heat exchanger simulation software. Preliminary results show that the heat recovery efficiency can be dramatically increased by using high thermal conductivity gases such as hydrogen and helium as the filler gas.